There are several instances where it is desirable to be able to deflect or control the direction of a borehole or to drill a new hole in any desired direction and at any desired level out of the axis of an existing borehole. For example, obstacles may be encountered in the course of drilling through which the drill bit cannot pass or through which it is undesirable for the drill bit to pass. Further, for various reasons a drill string may deflect of its own accord and it may then be required to bring the hole back into the vertical. Another important area where deflection is required is in obtaining core samples at various levels of an existing borehole. The absence of existing technology has made this last area generally impractical to date. Finally, an exploration group may wish to examine a formation of interest some distance removed from an existing hole. Present technology for achieving this objective suffers from serious shortcomings.
In general two methods have been utilized to achieve this deflection above the bottom of an existing hole. First, the whipstock method comprises the insertion into the borehole of wedges of various configurations which then deflect the drill bit in the desired direction. There are a substantial number of disadvantages to the use of the whipstock method. These include limitations on the bit styles and boring methods that can be used, primarily because of the contact of the bit with the durable surface of the whipstock, which wedges or jams the bit into the adjacent formation. Substantial extra time is required when using whipstocks, including extra trips into the hole to set and retrieve the whipstock.
The second method which has been utilized to obtain deflected or directional drilling is the use of a deployable member or element which is deployed adjacent the bit to press against the side of the hole to influence the bit to deflect. While these methods have provided some improvement, a number of substantial disadvantages remain. For example, in a number of these cases the deflection provided by the weight of the drill string on the bottom of the hole is a required element. In other cases the continued deployment of the deflection member or element is completely reliant on differential hydraulic pressure in the circulating drilling fluid.
Of substantial significance, earlier methods utilizing the deflection element deployment technique have generally been applicable to the bottom of the drill hole only. Furthermore, the deflection apparatus in these methods has moved downhole with the bit and the drill string. The present apparatus provides a deflection member or element which operates independently of drill string rotations and longitudinal movement and of fluid pressure in the drill string. It does not limit the type of bit to be utilized. The apparatus acts as an independent non-moveable anchor in the borehole allowing the drill string to pass through. It enables, for example, a sizable core sample to be obtained at any level of an existing borehole.